A cardiac stimulator of the aforementioned type typically has at least one right-ventricular sensing unit and one right-ventricular stimulation unit, plus one left-ventricular sensing unit and one left-ventricular stimulation unit. These units are connected by electrode lines to electrodes situated at suitable locations in the heart during operation of the cardiac stimulator. A left-ventricular electrode line typically bears the electrodes for detecting electric potentials in, and delivering stimulation pulses to, the left ventricle of the heart. The left-ventricular electrode line is usually implanted through the coronary sinus of the heart, and therefore is also referred to as a coronary sinus electrode line, though it may instead be an epicardial or endocardial electrode line to the left ventricle. The electrodes for detecting electric potentials in, and delivering stimulation pulses to, the right ventricle are typically attached to a right-ventricular electrode line whose distal end is situated at the apex of the right ventricle. The electrode lines are typically connected at their proximal end to a cardiac stimulator via standardized plug connections.
Typical stimulation modes for a right-ventricular cardiac stimulator, e.g., VVI, VVD or DDD, are well-known. The same is also true regarding modes for delivery of stimulation pulses only in case of need (demand pacemaker modes), in which delivery of a stimulation pulse to a particular chamber of the heart is suppressed when an assigned sensing unit of the cardiac stimulator has detected an intrinsic pulse in the chamber during a corresponding escape interval. These known concepts may be implemented with the cardiac stimulator described here.
Automatic (non-stimulated) contractions of a particular cardiac chamber are also referred to as intrinsic events, sense events, or intrinsic cardiac activities. They may be detected in a known manner by corresponding sensing units, which are connected to a particular electrode for detecting myocardial potentials during operation. In order for a particular sensing unit to avoid impairment by a potential due to the delivery of a stimulation pulse, sensing units are typically designed so that they do not detect any events within a short blanking period following a stimulus. Delivery of a stimulation pulse is also known as a pace event.
In common cardiac resynchronization therapy methods, to correct a dys-synchronicity of the right and left ventricles, the ventricles are electrically stimulated in order to ensure a defined interventricular delay time (VV delay, or VVD). This is true even with intact AV conduction, i.e., with natural conduction of a stimulus triggering a contraction from the atrium to the ventricle over the AV node. This methodology foregoes a more efficient contraction of the intrinsically stimulable ventricle and the associated natural regulation of AV delay (which also reflects physical exertion, for example).
US Published Patent Appln. 2009/0125077 proposes a cardiac stimulator which can automatically switch between a plain right-ventricular stimulation mode and a biventricular stimulation mode of the aforementioned type.